Process for producing vinyl acetate

ABSTRACT

THE PRODUCTION OF VINYL ACETATE BY SUBJECTING A GAS MIXITURE CONTAINING ETHYLENE, ACETIC ACID AND A MOLECULAR OXYGEN CONTAINING GAS TO CA CATALYTIC GAS PHASE REACTION AT A TEMPERATURE OF FROM 50* TO 300*C. IN THE PRESENCE OF A CATALYST COMPOSITION CONSISTING OF (A) AT LEAST ONE METAL OF PALLADIUM, RHODIUM, RUTHENIUM, PLATINUM AND IRIDUM; (B) AT LEAST ONE OF THE METALS, OXIDES, CHLORIDES, FORMATES AND ACETATES FO CADMIUM, ZINC AND URANIUM; (C) AT LEAST ONE OF THE CHLORIDES AND BROMIDES OF ALKALI METALS; AND (D) AT LEAST ONE OF THE ACETATES FO ALKALI METALS.

United States Patent PROCESS FOR PRODUCING VINYL ACETATE Naoya Kominami, 27-63, 3-chome, Nakadai, Itabashiku, Tokyo, Japan; Hitoshi Nakajima, 2716 Aza-oyama,

Ooaza-Kawarabuki, Ageo-shi, Saitama-ken, Ageo-shi,

Japan; Nobuhiro Tamura, 11-21, 6-chome, Sakuradai,

Nerima-ku, Tokyo, Japan; and Kusuo Ohki, 224

Shirako, Yamatomachi, Kita-adachi-gun, Saitama-ken,

Yamatomachi, Japan No Drawing. Filed June 4, 1968, Ser. No. 734,203

Claims priority, application Japan, Sept. 7, 1967, 42/57,163; Mar. 26, 1968, 43/9,195 Int. Cl. C07c 69/14 US. Cl. 260-497 A 4 Claims ABSTRACT OF THE DISCLOSURE The production of vinyl acetate by subjecting a gas mixture containing ethylene, acetic acid and a molecular oxygen containing gas to a catalytic gas phase reaction at a temperature of from 50 to 300 C. in the presence of a catalyst composition consisting of (A) at least one metal of palladium, rhodium, ruthenium, platinum and iridium; (B) at least one of the metals, oxides, chlorides, for-mates and acetates of cadmium, Zinc and uranium; (C) at least one of the chlorides and bromides of alkali metals; and (D) at least one of the acetates of alkali metals.

This invention relates to a process for producing vinyl acetate by gas phase reaction of ethylene, acetic acid and a molecular oxygen containing gas as starting materials.

The synthesis of vinyl acetate may be effected by subjecting a gas mixture containing ethylene, acetic acid and a molecular oxygen containing gas to a catalytic gas phase reaction at a temperature of from 50 to 300 C. in the presence of a catalyst composition containing of at least one of the metals palladium, platinum, rhodium, ruthenium and iridium as a main catalyst component, and at least one of the metals and oxides of copper, silver, zinc, cadmium, tin, lead, chromium, molybdenum, tungsten, iron, cobalt and nickel as a promoter, supported on a carrier (British Pat. No. 1,003,499).

However, it has been found that the above-mentioned process has a disadvantage in that the activity of the catalyst tends to decrease gradually for a prolonged re- Patented Jan. 11, 1972 "ice action period. Although it is still possible to practise the above-mentioned process commercially even with the use of catalysts having such tendency to decrease in activity, the process involves the provision of equipment and operations for regenerating catalysts or recharging fresh catalysts. In addition, the loss of catalysts in the regeneration operation is disadvantageous from the economic point of view since these catalysts are very expensive.

The phenomenon of decrease in catalyst activity has been investigated and it has been discovered that the addition of at least one of the chlorides, bromides and fluorides of alkali metal to the above-mentioned catalyst compositions may reduce substantially such decrease in catalyst activity and may prolong very greatly the life of catalyst. However, according to these processes, the one pass yield of vinyl acetate is excellent but a considerable amount of acetaldehyde is by-produced, and the selectivity of vinyl acetate based on the converted carbon atom is accordingly not always high and the provision of operations for separating the by-produced acetaldehyde from vinyl acetate is required.

Other processes hitherto proposed for producing vinyl acetate include a process carried out in the liquid phase at elevated temperatures using a palladium metal as a catalyst supported on a carrier in the presence of potassium acetate from ethylene, acetic acid and oxygen as starting materials (British Pat. No. 981,987) and a process carried out in the gas phase at elevated temperatures using a palladium metal catalyst containing an alkali metal acetate and/or an alkaline earth metal acetate from ethylene, acetic acid and oxygen as starting materials (British Pat. No. 1,017,938). The process of British Pat. No. 981,987 suffers from the drawbacks that the catalyst is required in large amount for producing a desired amount of vinyl acetate because the space time yield is low. The process of British Pat. No. 1,017,938 is good in selectivity of vinyl acetate, but low in conversion of ethylene and the space time yield is accordingly very low.

Table 1 below shows a comparison in catalyst activity among the above-mentioned catalysts in the gas phase reaction and the catalyst of the present invention. It will be easily understood that the catalyst of the present invention is much further improved in conversion of ethylene and in one pass yield and selectivity of vinyl acetate.

TABLE 1 One pass One pass One pass yield of Space time yield of yield of Selectivity Conversion vinyl yield of acetalcarbon of vinyl of ethylene acetate 1 vinyl dehyde dioxide acetate (mol (mol acetate (mol (mol (mol Catalyst composition percent) percent) (g./l. hr.) percent) percent) percent) a Pd-Silica -KOOCCH 6. 1 4. 9 13. 1 2. 4 80. 4

(Pd-KCl-Silica) 6 9. 8 6. 1 16. 3 3. 2 1.0 62. 3 (Pd-Zn-KCl-Silica) 5 11. 4 0. 8 18. 2 3. 8 0. 8 59. 7

3 (Pd-Zn-KCl-SilicaKOOCCHa 0 10. 8 8. 7 23. 3 4. 2 80. 5

1 Based on the fed ethylene. 2 Based on the converted ethylene.

B Prepared in the same manner as in Example 2.

Reaction conditions:

Catalyst-30 cc.: Palladium metal content 2.0 wt. percent; Potassium metal content 2.0 wt. percent; Zine metal content 0.4 wt. percent (in each catalyst) Reaction temperature 150 0. Space velocityhrr Pressure-Atmospheric.

Results: Over 24 hours after the start of the reaction.

It is, therefore, an object of this invention to provide a process for the production of vinyl acetate from ethylene, acetic acid and a molecular oxygen containing gas in a catalytic gas phase reaction in the presence of a suitable catalyst composition with a very greatly prolonged life of catalyst in high yields and at high selectivity, efficiently and economically.

According to the present invention a process for producing vinyl acetate comprises subjecting a gas mixture containing ethylene, acetic acid and a molecular oxygen containing gas to a catalytic gas phase reaction at a temperature of from 50 to 300 C. in the presence of a catalyst composition consisting of at least one of the metals of palladium, rhodium, ruthenium, platinum and iridium; at least one of the metals, oxides, chlorides, acetates and formates of cadmium, zinc and uranium; at least one of the chlorides and bromides of alkali metals; and at least one of the acetates of alkali metals.

The atomic ratio of the cadmium, zinc and uranium metal of the cadmium, zinc and uranium metals, oxides, chlorides, formates and acetates to the metal of palladium, rhodium, ruthenium, platinum and iridium as the main catalyst component is in the range of 0.01l: I, preferably 0.0530:l and most preferably 0.ll0: 1.

Examples of the chlorides, bromides and acetates of alkali metals which may be used in the process of this invention are those of lithium, sodium, potassium, rubidium and cesium.

The atomic ratio of the alkali metal of the alkali metal chlorides and bromides to the metal of the main catalyst component is in the range of 0.1100:1, preferably 0.5-30z1, most preferably 110:l.

The atomic ratio of the alkali metal of the alkali metal acetate to the main catalyst component is in the range of 0.1-10021, and preferably 0.5-20zl.

In preparing the catalyst for use in the process of this invention any of the conventional methods such as immersing method, mixing method, precipitating method or calcing method may be employed. For example, a catalyst composition consisting of platinum, zinc, potassium chloride and sodium acetate employed in the process of this invention may be obtained by preparing a mixture solution containing a desired amount of chloroplatinic acid, zinc chloride and potassium chloride, supporting them on a carrier by immersion, reducing them sufiiciently with a reducing agent such as hydrogen, hydrazine or formaldehyde and subsequently immersing the resultant mixture in an aqueous potassium acetate solution and evaporating the composition thus treated to dryness. The catalyst composition may be reduced at any step prior to the addition of at least one of cadmium, zinc, uranium formates, acetates and alkali metal acetates in the course of the preparation of catalyst.

The use of a carrier is not essential but is advantageous and preferable examples of carriers are active carbon, silica, silica-alumina, alumina, titania, boria, aluminaboria and silicon carbide. Silica and active carbon are preferred.

In practising the process of this invention, no particular range of mol ratio of ethylene to oxygen is necessarily required. A mol ratio of ethylene to oxygen of 1:1 to 50:1 is preferred. Likewise, although no particular range is imposed on the proportion of ethylene to acetic acid, a mol ratio of ethylene to acetic acid of 50:1 to 1:10 is preferred.

The space velocity of the gas mixture containing ethylene, acetic acid and a molecular oxygen containing gas is preferably from 30 to 5000 hr. and most preferably ranges from about 50 to about 800 hrf In the process of this invention, a reaction temperature is in the range of from 50 to 300 C., preferably from 80 to 200 C. At a temperature below 50 C. the rate of reaction is undesirably low, whereas at a temperature above 300 C. the side-reactions become active and the 4 selectivity of vinyl acetate is accordingly remarkably reduced.

The ethylene used as starting material may contain a small amount of low saturated aliphatic hydrocars such as methane, ethane and propane.

Oxygen, pure or diluted with an inert gas such as nitrogen and carbon dioxide, or air may be employed as a molecular oxygen containing gas.

The reaction pressure may either be atmospheric or superatmospheric pressure so long as both the starting gases and reaction product gases are maintained at gas phase under the reaction conditions of the process of this invention.

Fixed, moving or fluidized bed systems may be employed in the reaction of the process of this invention.

This invention is further illustrated by the following examples which are in no way limiting upon the scope thereof.

EXAMPLE 1 300 cc. of granular silica gel of 5 to 15 mesh was added to an aqueous hydrochloric acid solution containing 2.7 g. of palladium chloride, 2.0 g. of zinc chloride and 10 g. of potassium chloride, and the mixture was evaporated to dryness on a hot water bath, reduced slowly with cc. of an aqueous solution containing 30 cc. of hydrazine hydrate, washed with Water, dried, subsequently immersed in an aqueous solution containing 5.9 g. of potassium acetate and evaporated to dryness. The resulting catalyst was charged together with quartz sand into a U-tube of stainless steel having 28 mm. inside diameter and 1.5 m. length and dried at 150 C. for 12 hours While introducing nitrogen. A gas mixture consisting of ethylene, acetic acid and oxygen at a ratio of 193 l./m., 96.5 l./m. and 36.2 l./m. (at normal temperature and pressure) was fed to the reaction tube maintained at 150 C. at a gauge pressure of 6 kg./cm. Over 24 hours after the start of the reaction the space time yield of vinyl acetate was g./l. hr., and 98.5% of the converted vinyl acetate was vinyl acetate, and the rest was carbon dioxide.

For comparison, the procedure of Example 1 was repeated using the identical reactor and'reaction conditions except that the catalyst composition (PdSilica-KOOCCH prepared by supporting 2.7 g. of palladium chloride on 300 cc. of silica gel followed by treating the resulting mixture in the same manner as in Example 1 was employed. Over 24 hours after the start of the reaction the space time yield of vinyl acetate was 64 g./l. hr. and the rest was carbon dioxide.

EXAMPLE 2 2.7 g. of palladium chloride and 3.8 g. of sodium bromide were supported on 300 cc. of silica gel by the immersion method, reduced in the same manner as in Example 1, subsequently immersed in 2.3 g. of uranium acetate and 5.9 g. of potassium acetate and evaporated to dryness. The procedure of Example 1 was repeated using the resulting catalyst composition, the identical reactor and reaction conditions, and over 24 hours after the start of the reaction the space time yield of vinyl acetate was 97 g./l. hr. and 99.2% of the converted acetic acid was vinyl acetate.

EXAMPLES 3-24 The reaction was carried out using the same reactor as in Example 1 and each catalyst composition was prepared by the same immersion method as in Example 1. Table 2 shows the reaction conditions and results over 24 hours after the start of the reaction.

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References Cited UNITED STATES PATENTS 3,190,912 6/1965 Robinson 260497 1 Q F ORElGN PATENTS 618,07 1- 9/ 1962 Belgium 260497 1,407,526 6/1965 France 260497 25/11,?171 1965 Japan 260497 LORRAINE A. WEINBERGER, Primary Examiner R. D. KELLY, Assistant Examiner 

